Rabbit cultured aorta endothelial cells were shown to deaminate a variety of vasoactive monoamines including, norepinephrine, dopamine, tyramine, phenylethylamine and 5-hydroxytryptamine. These cells were found to contain both the A and B form of mitochondrial monoamine oxidase (MAO). Based on selective MAO inhibitor studies with the drug, clorgyline, it was demonstrated that the B form of the oxidase predominates in these cells. This is in direct contrast to cultured fibroblasts from rabbit aorta which were found to contain exclusively the A species of MAO. In addition to the above studies, experiments are presently underway to measure and characterize the monoamine transport systems in the cultured endothelial cells. A comparison of these processes will also be made with cultured fibroblasts and smooth muscle cells isolated from same rabbit tissue. Other studies involve quantitization and characterization of the adrenergic receptors on various cultured cells derived from the vascular wall. It is anticipated that these studies will lead to a better understanding of the role that endothelium and the other cell types have in controlling and responding to the vasoactive amines.